Installation & Operation Manual
11
4
Domestic Side (Tank) Piping
Basic Domestic Piping
Figure 4-2 on page 14 shows typical domestic water piping
for a tank. The function of the components shown are as
follows:
a. Shut-off valves (recommended) - Used to isolate the
tank for servicing.
b. Backflow Preventer (required by some codes) - Used to
prevent water from backing out of the tank and into
the main potable water supply in the event that inlet
water pressure drops.
c. Expansion Tank (required for thermal expansion) -
This expansion tank absorbs the increased volume
caused by heating water.
Use an expansion tank designed for use on domestic
water systems. Refer to the expansion tank
manufacturer’s literature for the proper size expansion
tank to use.
NOTICE
If an expansion tank is used, do not put
any valves between the expansion tank
and tank inlet.
d. Unions (optional) - Used to disconnect the tank in the
unlikely event that this is necessary.
e. Drain (required) - Used to drain the tank for
inspection or servicing.
Multiple Tank Domestic Water Piping
The two pipe reverse return piping uses more pipe than the
two pipe direct return piping, but the flow is more balanced
and even in the two pipe reverse return piping layout (see
FIG. 3-4).
Each tank must have its own T&P valve. It is recommended
that each tank be equipped with its own isolation valves,
unions, and drains so that one tank may be removed from
the system. If local codes require a backflow preventer,
check with the appropriate authority to find out whether
one backflow preventer may be used for tanks or each tank
must be equipped with its own backflow preventer. If each
tank must have its own backflow preventer, each tank must
also have its own expansion tank. If a common backflow
preventer is permitted, an expansion tank must be sized to
accommodate the expansion volume of all tanks.
Because hot water is always circulating in the hot water
branch, the entire branch should be insulated to prevent
excessive heat loss.
Domestic Water Piping for Distant Fixtures
In some cases the furthest fixture may be quite distant
from the tank. Such an installation would result in an
unacceptable delay before hot water reaches these distant
fixtures. Even if all the fixtures are relatively close to the
tank, the building owner may want hot water at all fixtures
as soon as they are opened.
To prevent delays, return circulation piping with a check
valve that allows flow to the inlet of the tank. This should
be installed on each branch circuit at the farthest fixture or
device, so that hot water is supplied upon demand.
